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ETHER

59

thermometer, z>.,ione that has been calibrated, and the o ancl IOOQ
points carefully determined. An ordinary thermometer corrected
by a standard thermometer at Kew will serve equally well.
Correction must also be made for barometic pressure. This is
approximately 0-043 for every I mm. below 76o-(Landolt). A
further correction is required for the thread of mercury, which
may project above the vessel. For this correction the following-
formula may be used :

N(T-/)o*oooi54.

Where T = apparent temperature in degrees.

/ = temperature of a second thermometer, the bulb
of which is placed at half the length N above
the vessel.
N = length of the mercury column in degrees from

above the vessel to T.
0*000154 = apparent expansion of mercury in glass.

This correction may be avoided by using short (Anschiitz)
thermometers, in which the mercury thread is entirely immersed
in the vapour. A rough correction for points above 100 may
be made by determining the boiling points of pure organic
substances, such as naphthalene, 2i6'6, &c.

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PREPARATION 3.
Ether (Diethyl Ether, Diethyl Oxide), (C2H5).2O
V. Cordus (1544); Jottrn. Pharm^ 1815, 1, 97 ; Williamson,
Phil Mag. 1850, (3)37, 35.
150 grms. (80 c.c.) cone, sulphuric acid.
85         (no c.c.) absolute alcohol.
A distilling flask (\ litre) is fitted with a double-bored cork.
Through one hole a thermometer is inserted, the bulb of which
must be covered by the liquid in the flask and through the
other a tap-funnel passes. The side-tube of the distilling flask
is fixed by a cork into the upper end of a long condenser. An
adapter is fitted to the lower end and passes through the neck
of a flask, which is surrounded by ice. The apparatus is shown